Substrate holder, lithographic apparatus, device manufacturing method, and method of manufacturing a substrate holder

ABSTRACT

A substrate holder for a lithographic apparatus has a planarization layer provided on a surface thereof. The planarization layer provides a smooth surface for the formation of an electronic component such as a thin film electronic component. The planarization layer may be provided in multiple sub layers. The planarization layer may smooth over roughness caused by removal of material from a blank to form burls on the substrate holder.

This application is a continuation of U.S. patent application Ser. No.16/376,673, filed Apr. 5, 2019, now allowed, which is a continuation ofU.S. patent application Ser. No. 15/994,492, filed on May 31, 2018, nowU.S. Pat. No. 10,254,660, which is a continuation of U.S. patentapplication Ser. No. 15/587,086, filed on May 4, 2017, now U.S. Pat. No.9,989,867, which is a continuation of U.S. patent application Ser. No.15/233,775, filed on Aug. 10, 2016, now U.S. Pat. No. 9,678,445, whichis a continuation of U.S. patent application Ser. No. 13/323,520, filedon Dec. 12, 2011, now U.S. Pat. No. 9,423,699, which claims priority andbenefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent ApplicationNo. 61/422,918, filed on Dec. 14, 2010. The content of each of theforegoing applications is incorporated herein in its entirety byreference.

FIELD

The present invention relates to a substrate holder, a lithographicapparatus, a device manufacturing method, and a method of manufacturinga substrate holder.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe present invention will be described with reference to liquid.However, another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

SUMMARY

In a conventional lithography apparatus, the substrate to be exposed maybe supported by a substrate holder which in turn is supported by asubstrate table. The substrate holder is often a flat rigid disccorresponding in size and shape to the substrate (although it may have adifferent size or shape). It has an array of projections, referred to asburls or pimples, projecting from at least one side. In an embodiment,the substrate holder has an array of projections on two opposite sides.In this case, when the substrate holder is placed on the substratetable, the main body of the substrate holder is held a small distanceabove the substrate table while the ends of the burls on one side of thesubstrate holder lie on the surface of the substrate table. Similarly,when the substrate rests on the top of the burls on the opposite side ofthe substrate holder, the substrate is spaced apart from the main bodyof the substrate holder. The purpose of this is to help prevent aparticle (i.e. a contaminating particle such as a dust particle) whichmight be present on either the substrate table or substrate holder fromdistorting the substrate holder or substrate. Since the total surfacearea of the burls is only a small fraction of the total area of thesubstrate or substrate holder, it is highly probable that any particlewill lie between burls and its presence will have no effect. Often, thesubstrate holder and substrate are accommodated within a recess in thesubstrate table so that the upper surface of the substrate issubstantially coplanar with the upper surface of the substrate table.

Due to the high accelerations experienced by the substrate in use of ahigh-throughput lithographic apparatus, it is not sufficient to allowthe substrate simply to rest on the burls of the substrate holder. It isclamped in place. Two methods of clamping the substrate in place areknown—vacuum clamping and electrostatic clamping. In vacuum clamping,the space between the substrate holder and substrate and optionallybetween the substrate table and substrate holder are partially evacuatedso that the substrate is held in place by the higher pressure of gas orliquid above it. Vacuum clamping however may not be used where the beampath and/or the environment near the substrate or substrate holder iskept at a low or very low pressure, e.g. for extreme ultraviolet (EUV)radiation lithography. In this case, it may not be possible to develop asufficiently large pressure difference across the substrate (orsubstrate holder) to clamp it. Electrostatic clamping may therefore beused. In electrostatic clamping, a potential difference is establishedbetween the substrate, or an electrode plated on its lower surface, andan electrode provided on the substrate table and/or substrate holder.The two electrodes behave as a large capacitor and substantial clampingforce can be generated with a reasonable potential difference. Anelectrostatic arrangement can be such that a single pair of electrodes,one on the substrate table and one on the substrate, clamps together thecomplete stack of substrate table, substrate holder and substrate. In anarrangement, one or more electrodes may be provided on the substrateholder so that the substrate holder is clamped to the substrate tableand the substrate is separately clamped to the substrate holder.

It is desirable to provide one or more electronic components on thesubstrate holder. For example, it is desirable to provide one or moreheaters on the substrate holder to enable localized control of thetemperature of the substrate and substrate holder. It is desirable toprovide one or more sensors, e.g. a temperature sensor to measure thelocal temperature of the substrate holder and/or substrate. It isdesirable to provide an electrode for an electrostatic clamp on thesubstrate holder. Such components could be accommodated on the surfaceof the substrate holder between the burls. However, the surface of thesubstrate holder may be too rough to allow reliable formation of one ormore electronic components thereon. The roughness of the surface of thesubstrate holder is due to the use of processes such as etching, laserablation and electron beam machining to remove material to form theburls.

It is desirable to provide a substrate holder on which one or moreelectronic components, such as one or more thin-film components, can bereliably formed.

According to an aspect of the invention, there is provided a substrateholder for use in a lithographic apparatus, the substrate holdercomprising: a main body having a surface; a plurality of burlsprojecting from the surface and having end surfaces to support asubstrate; and a planarization layer provided on at least part of themain body surface.

According to an aspect of the invention, there is provided alithographic apparatus, comprising: a support structure configured tosupport a patterning device; a projection system arranged to project abeam patterned by the patterning device onto a substrate; and asubstrate holder arranged to hold the substrate, the substrate holdercomprising: a main body having a surface, a plurality of burlsprojecting from the surface and having end surfaces to support asubstrate, and a planarization layer provided on at least part of themain body surface.

According to an aspect of the invention, there is provided a devicemanufacturing method using a lithographic apparatus, the methodcomprising:

holding a substrate on a substrate holder, the substrate holdercomprising: a main body having a surface, a plurality of burlsprojecting from the surface and having end surfaces to support asubstrate, and a planarization layer provided on at least part of themain body surface; and

projecting a beam patterned by a patterning device onto the substratewhile held by the substrate holder.

According to an aspect of the invention, there is provided a method ofmanufacturing a substrate holder for use in a lithographic apparatus,the method comprising:

providing a main body having a surface and a plurality of burlsprojecting from the surface and having end surfaces to support asubstrate; and

forming a planarization layer on at least part of the main body surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, a barrier member which may be used inan embodiment of the present invention as an immersion liquid supplysystem;

FIG. 6 depicts in cross-section a substrate table and a substrate holderaccording to an embodiment of the invention;

FIG. 7 is an enlarged view of a part of the substrate holder of FIG. 6;

FIG. 8 is a further enlarged view of a part of the substrate holder ofFIGS. 6 and 7;

FIGS. 9 and 10 depict steps in a method of manufacturing a substrateholder according to an embodiment of the invention;

FIGS. 11 to 14 depict steps in a method of manufacturing a substrateholder according to an embodiment of the invention;

FIG. 15 is a graph depicting surface roughness of some examples of anembodiment of the invention; and

FIGS. 16 to 19 depict chemical reactions in formation of planarizationlayers in embodiments of the invention. Note that conversion of apolysilazane with chains of —Si—N— backbones to Si—O— backbones may notcomplete, i.e. reach 100%. A resulting planarization layer after curingmay have a low concentration of —Si—N— chains.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation, DUV radiation or EUV        radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT holds the patterning device. The supportstructure MT holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structureMT can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure MT maybe a frame or a table, for example, which may be fixed or movable asrequired. The support structure MT may ensure that the patterning deviceis at a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more patterning device tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM configured to adjust theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL may comprise various other components, such as anintegrator IN and a condenser CO. The illuminator may be used tocondition the radiation beam, to have a desired uniformity and intensitydistribution in its cross-section. Similar to the source SO, theilluminator IL may or may not be considered to form part of thelithographic apparatus. For example, the illuminator IL may be anintegral part of the lithographic apparatus or may be a separate entityfrom the lithographic apparatus. In the latter case, the lithographicapparatus may be configured to allow the illuminator IL to be mountedthereon. Optionally, the illuminator IL is detachable and may beseparately provided (for example, by the lithographic apparatusmanufacturer or another supplier).

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-) magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

In many lithographic apparatus a fluid, in particular a liquid forexample an immersion lithographic apparatus, is provided between thefinal element of the projection system using a liquid supply system IHto enable imaging of smaller features and/or increase the effective NAof the apparatus. An embodiment of the invention is described furtherbelow with reference to such an immersion apparatus, but may equally beembodied in a non-immersion apparatus. Arrangements to provide liquidbetween a final element of the projection system and the substrate canbe classed into at least two general categories. These are the bath typearrangement and the so called localized immersion system. In the bathtype arrangement substantially the whole of the substrate and optionallypart of the substrate table is submersed in a bath of liquid. The socalled localized immersion system uses a liquid supply system in whichliquid is only provided to a localized area of the substrate. In thelatter category, the space filled by liquid is smaller in plan than thetop surface of the substrate and the area filled with liquid remainssubstantially stationary relative to the projection system while thesubstrate moves underneath that area. Anther arrangement, to which anembodiment of the invention is directed, is the all wet solution inwhich the liquid is unconfined. In this arrangement substantially thewhole top surface of the substrate and all or part of the substratetable is covered in immersion liquid. The depth of the liquid coveringat least the substrate is small. The liquid may be a film, such as athin film, of liquid on the substrate.

Four different types of localized liquid supply systems are illustratedin FIGS. 2-5. Any of the liquid supply devices of FIGS. 2-5 may be usedin an unconfined system; however, sealing features are not present, arenot activated, are not as efficient as normal or are otherwiseineffective to seal liquid to only the localized area.

One of the arrangements proposed for a localized immersion system is fora liquid supply system to provide liquid on only a localized area of thesubstrate and in between the final element of the projection system andthe substrate using a liquid confinement system (the substrate generallyhas a larger surface area than the final element of the projectionsystem). One way which has been proposed to arrange for this isdisclosed in PCT patent application publication no. WO 99/49504. Asillustrated in FIGS. 2 and 3, liquid is supplied by at least one inletonto the substrate, desirably along the direction of movement of thesubstrate relative to the final element, and is removed by at least oneoutlet after having passed under the projection system. That is, as thesubstrate is scanned beneath the element in a −X direction, liquid issupplied at the +X side of the element and taken up at the −X side.

FIG. 2 shows the arrangement schematically in which liquid is suppliedvia inlet and is taken up on the other side of the element by outletwhich is connected to a low pressure source. The arrows above thesubstrate W illustrate the direction of liquid flow, and the arrow belowthe substrate W illustrates the direction of movement of the substratetable. In the illustration of FIG. 2 the liquid is supplied along thedirection of movement of the substrate relative to the final element,though this does not need to be the case. Various orientations andnumbers of in-and out-lets positioned around the final element arepossible, one example is illustrated in FIG. 3 in which four sets of aninlet with an outlet on either side are provided in a regular patternaround the final element. Arrows in liquid supply and liquid recoverydevices indicate the direction of liquid flow.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletsand outlets can be arranged in a plate with a hole in its center andthrough which the projection beam is projected. Liquid is supplied byone groove inlet on one side of the projection system PS and removed bya plurality of discrete outlets on the other side of the projectionsystem PS, causing a flow of a thin film of liquid between theprojection system PS and the substrate W. The choice of whichcombination of inlet and outlets to use can depend on the direction ofmovement of the substrate W (the other combination of inlet and outletsbeing inactive). In the cross-sectional view of FIG. 4, arrowsillustrate the direction of liquid flow in inlets and out of outlets.

Another arrangement which has been proposed is to provide the liquidsupply system with a liquid confinement member which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5. The liquid confinement member is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). A seal is formed between the liquid confinementand the surface of the substrate. In an embodiment, a seal is formedbetween the liquid confinement structure and the surface of thesubstrate and may be a contactless seal such as a gas seal. Such asystem is disclosed in United States patent application publication no.US 2004-0207824.

FIG. 5 schematically depicts a localized liquid supply system with afluid handling structure 12. The fluid handling structure extends alongat least a part of a boundary of the space between the final element ofthe projection system and the substrate table WT or substrate W. (Pleasenote that reference in the following text to surface of the substrate Walso refers in addition or in the alternative to a surface of thesubstrate table, unless expressly stated otherwise.) The fluid handlingstructure 12 is substantially stationary relative to the projectionsystem in the XY plane though there may be some relative movement in theZ direction (in the direction of the optical axis). In an embodiment, aseal is formed between the barrier member and the surface of thesubstrate W and may be a contactless seal such as a fluid seal,desirably a gas seal.

The fluid handling structure 12 at least partly contains liquid in thespace 11 between a final element of the projection system PS and thesubstrate W. A contactless seal 16 to the substrate W may be formedaround the image field of the projection system so that liquid isconfined within the space between the substrate W surface and the finalelement of the projection system PS. The space is at least partly formedby the fluid handling structure 12 positioned below and surrounding thefinal element of the projection system PS. Liquid is brought into thespace below the projection system and within the fluid handlingstructure 12 by liquid inlet 13. The liquid may be removed by liquidoutlet 13. The fluid handling structure 12 may extend a little above thefinal element of the projection system. The liquid level rises above thefinal element so that a buffer of liquid is provided. In an embodiment,the fluid handling structure 12 has an inner periphery that at the upperend closely conforms to the shape of the projection system or the finalelement thereof and may, e.g., be round. At the bottom, the innerperiphery closely conforms to the shape of the image field, e.g.,rectangular, though this need not be the case.

In an embodiment, the liquid is contained in the space 11 by a gas seal16 which, during use, is formed between the bottom of the fluid handlingstructure 12 and the surface of the substrate W. The gas seal is formedby gas, e.g. air or synthetic air but, in an embodiment, N₂ or anotherinert gas. The gas in the gas seal is provided under pressure via inlet15 to the gap between fluid handling structure 12 and substrate W. Thegas is extracted via outlet 14. The overpressure on the gas inlet 15,vacuum level on the outlet 14 and geometry of the gap are arranged sothat there is a high-velocity gas flow 16 inwardly that confines theliquid. The force of the gas on the liquid between the fluid handlingstructure 12 and the substrate W contains the liquid in a space 11. Theinlets/outlets may be annular grooves which surround the space 11. Theannular grooves may be continuous or discontinuous. The flow of gas 16is effective to contain the liquid in the space 11. Such a system isdisclosed in United States patent application publication no. US2004-0207824.

The example of FIG. 5 is a so called localized area arrangement in whichliquid is only provided to a localized area of the top surface of thesubstrate W at any one time. Other arrangements are possible, includingfluid handling systems which make use of a single phase extractor or atwo phase extractor as disclosed, for example, in United States patentapplication publication no US 2006-0038968.

Another arrangement which is possible is one which works on a gas dragprinciple. The so-called gas drag principle has been described, forexample, in United States patent application publication no. US2008-0212046, United States patent application publication no. US2009/0279060 and United States patent application publication no. US2009/0279062. In that system the extraction holes are arranged in ashape which desirably has a corner. The corner may be aligned with thestepping or scanning directions. This reduces the force on the meniscusbetween two openings in the surface of the fluid handing structure for agiven speed in the step or scan direction compared to if the two outletswere aligned perpendicular to the direction of scan.

Also disclosed in US 2008-0212046 is a gas knife positioned radiallyoutside the main liquid retrieval feature. The gas knife traps anyliquid which gets past the main liquid retrieval feature. Such a gasknife may be present in a so called gas drag principle arrangement (asdisclosed in US 2008-0212046), in a single or two phase extractorarrangement (such as disclosed in United States patent applicationpublication no. US 2009-0262318) or any other arrangement.

Many other types of liquid supply system are possible. The presentinvention is neither limited to any particular type of liquid supplysystem, nor to immersion lithography. The invention may be appliedequally in any lithography. In an EUV lithography apparatus, the beampath is substantially evacuated and immersion arrangements describedabove are not used.

A control system 500 controls the overall operations of the lithographicapparatus and in particular performs an optimization process describedfurther below. Control system 500 can be embodied as asuitably-programmed general purpose computer comprising a centralprocessing unit, volatile and non-volatile storage means, one or moreinput and output devices such as a keyboard and screen, one or morenetwork connections and one or more interfaces to the various parts ofthe lithographic apparatus. It will be appreciated that a one-to-onerelationship between controlling computer and lithographic apparatus isnot necessary. In an embodiment of the invention one computer cancontrol multiple lithographic apparatuses. In an embodiment of theinvention, multiple networked computers can be used to control onelithographic apparatus. The control system 500 may also be configured tocontrol one or more associated process devices and substrate handlingdevices in a lithocell or cluster of which the lithographic apparatusforms a part. The control system 500 can also be configured to besubordinate to a supervisory control system of a lithocell or clusterand/or an overall control system of a fab.

FIG. 6 depicts a substrate holder 100 according to an embodiment of theinvention. It is held within a recess in substrate table WT and supportssubstrate W. The main body of the substrate holder 100A has the form ofa flat disc substantially corresponding in shape and size to thesubstrate W. At least on a top side, in an embodiment on both sides, thesubstrate holder has projections 106, commonly referred to as burls. Inan embodiment, the substrate holder is an integral part of the substratetable and does not have burls on the lower surface. The burls are notshown to scale in FIG. 6. In a practical embodiment, there can be manyhundreds of burls distributed across a substrate holder of diameter,e.g., 300 mm. The tips of the burls have a small area, e.g. less than 1mm², so that the total area of all of the burls on one side of thesubstrate holder 100 is less than about 1% of the total area of thetotal surface area of the substrate holder. In this way, there is a veryhigh probability that any particle that might lie on the surface of thesubstrate, substrate holder or substrate table will fall between burlsand will not therefore result in a deformation of the substrate orsubstrate holder. The arrangement of burls can be regular or can vary asdesired to provide appropriate distribution of force on the substrateand substrate table. The burls can have any shape in plan but arecommonly circular in plan. The burls can have the same shape anddimensions throughout their height but are commonly tapered. The burlscan project a distance of from about 1 μm to about 5 mm, desirably fromabout 10 μm to about 1 μm, from the rest of the surface of the main bodyof the substrate holder 100A. The thickness of the main body 100A of thesubstrate holder 100 can be in the range of about 20 mm to about 50 mm.

In an embodiment of the invention, the substrate holder 100 is made of anon-conducting rigid material. A suitable material includes SiC (siliconcarbide), SiSiC (siliconised silicon carbide), Si₃N₄ (silicon nitrite),quartz, and/or various other ceramic and glass-ceramics, such asZerodur™ glass ceramic. The substrate holder 100 can be manufactured byselectively removing material from a solid disc of the relevant materialso as to leave the projecting burls. A suitable technique to removematerial includes electrical discharge machining (EDM), etching and/orlaser ablation. These techniques leave a rough surface, e.g. having aroughness value Ra of the order of several microns. The minimumroughness achievable with these removal techniques may derive from thematerial properties. For example, in the case of a two-phase materialsuch as SiSiC, the minimum roughness achievable is determined by thegrain size of the two-phase material. Such residual roughness causesdifficulty in forming one or more electrical components, such as one ormore thin film components, on the surface of the substrate andunreliability in such components. These problems may arise because theroughness causes gaps and cracks in thin layers coated or grown on thesubstrate holder to form an electronic component. A thin film componentmay have a layer thickness in the range of from about 2 nm to about 50μm and may be formed by a process including chemical vapor deposition,physical vapor deposition (e.g. sputtering), dip coating, spin coatingand/or spray coating.

An electronic component to be formed on the substrate table can include,for example, an electrode, a resistive heater and/or a sensor, such as astrain sensor, a magnetic sensor, a pressure sensor or a temperaturesensor. A heater and sensor can be used to locally control and/ormonitor the temperature of the substrate holder and/or substrate so asto reduce undesired or induced desired temperature variation and stressin the substrate holder or substrate. It is desirable to controltemperature and/or stress of the substrate in order to reduce oreliminate imaging errors such as overlay errors due to local expansionor contraction of the substrate. For example, in an immersionlithography apparatus, evaporation of residual immersion liquid (e.g.,water) on the substrate may cause localized cooling and hence shrinkageof the substrate. Conversely, the energy delivered to the substrate bythe projection beam during exposure can cause significant heating andtherefore expansion of the substrate.

In an embodiment, the component to be formed is an electrode for anelectrostatic clamp. In electrostatic clamping, a potential differenceis established between the substrate, or an electrode plated on itslower surface, and an electrode provided on the substrate table and/orsubstrate holder. The two electrodes behave as a large capacitor andsubstantial clamping forces can be generated with a reasonable potentialdifference. An electrostatic arrangement can be such that a single pairof electrodes, one on the substrate table and one on the substrate,clamps together the complete stack of substrate table, substrate holderand substrate. In an arrangement, one or more electrodes may be providedon the substrate holder so that the substrate holder is clamped to thesubstrate table and the substrate separately clamped to the substrateholder.

In an embodiment, one or more localized heaters 101 are controlled bycontroller 103 to provide a desired amount of heat to the substrateholder 100 and substrate W to control the temperature of the substrateW. One or more temperature sensors 102 are connected to controller 104which monitors the temperature of the substrate holder 100 and/orsubstrate W. Voltage source 105 generates a potential difference e.g. ofthe order of 10 to 100 volts, between the substrate W and substratetable WT so that an electrostatic force clamps the substrate W,substrate holder 100 and substrate table WT together. In an embodiment,the potential difference is provided between an electrode on the lowersurface of the substrate W and an electrode on the bottom of the recessin the substrate table WT. Arrangements using one or more heaters andtemperature sensors to locally control the temperature of a substrateare described in U.S. patent application publication nos. US2011/0222032 and US 2011/0222033, which documents are incorporatedherein by reference in their entirety. The arrangements describedtherein can be modified to make use of a resistive heater andtemperature sensor as described herein.

FIG. 7 is an enlargement of part of the substrate holder 100 of FIG. 6showing the upper surface 107 and some burls 106 in cross-section. In anembodiment of the invention, a planarization layer 108 is provided onthe upper surface 107 in at least some areas between the burls 106. Inan embodiment, the planarization layer can be provided only where anelectronic component is to be formed or across substantially the entireupper surface of the substrate holder 100. FIG. 8 shows a furtherenlargement of the planarization layer 108. As can be seen, theplanarization layer fills in roughnesses of the upper surface 107 andprovides an upper surface 108 a that is substantially smoother than thesurface 107. In an embodiment of the invention the roughness Ra of thesurface 108 a is less than about 1.5 μm, desirably less than about 1 μm,or desirably less than about 0.5 μm.

In an embodiment, the planarization layer 108 is formed by applying aplurality, e.g. two, layers of coating material or precursor material.In an embodiment the planarization layer 108 is formed by applying asingle layer of coating material or precursor material. Depending uponthe material of the planarization layer it can be possible to determinefrom inspection of the formed coating that it has been applied byforming multiple sub-layers. In an embodiment, the multiple sub-layersof the planarization layer 108 are formed of the same material. In anembodiment, the multiple sub-layers of the planarization layer 108 areformed of different materials.

In an embodiment, the planarization layer 108 is formed of a siliconoxide or silicon nitride-based compound with a functional group attachedto each Si atom. The functional groups can be selected from the groupconsisting of hydrogen, methyl, fluoro, vinyl and the like. Suchmaterials are disclosed in U.S. Pat. No. 7,524,735, which document isincorporated herein in its entirety by reference. The precursor of thedielectric material may include one of more of the following compounds:triethoxysilane (TES), tetraethyl orthosilicate or tetra-ethoxy-silane(TEOS), tetramethoxysilane (TMOS), methyl triethoxysilane (MTEOS),methyltrimethoxysilane (MTMOS), dimethyldimethoxysilane (DMDMOS),trimethylmethoxysilane (TMMOS), dimethyldiethoxysilane (DMDEOS),bis-triethoxysilylethane (BTEOSE) or bis-triethoxysilylmethane (BTEOSM),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), and/or tetravinyltetramethylcyclotetrasiloxane (TVTMCTS). Incertain embodiments, the dielectric precursor is mixed in a carriersolvent, e.g., an alcohol. In an embodiment, the planarization layer 108is formed of Si(CH₃)₂O_(x) which may be formed from an organicprecursor. In an embodiment the planarization layer is formed of SiOx,e.g. SiO₂. In an embodiment the planarization layer is formed of anorganic monmomer (i.e. carbon-based material) such as benzocyclobutene(BCB). Other suitable materials include another oxide such as aluminumoxide and/or titanium oxide. Such oxides are desirably non conductive.Such an oxide layer may be formed from an organic pre-cursor. A methodof applying such a material is described in U.S. Pat. No. 7,524,735,which document is incorporated herein in its entirety by reference. Inan embodiment the planarization layer is formed of polymer chainsconsisting of Si(CH₃)₂N and Si(CH₃)₂O backbones. Methods of applying theplanarization layer include one or more coating techniques selectedfrom: deep-coating, spin coating, spray-coating and/or a depositiontechnique for example in a gasesous environment such as air or in avacuum.

The planarization layer may have a thickness in the range of from about0.2 μm to about 200 μm, desirably from about 2 μm to about 20 μm. In anembodiment the planarization layer is about 10 μm. The thickness of theplanarization layer is the thickness of such a coating as determined bythe same volume of coating applied to a substrate of silicon, e.g. asilicon wafer used in the lithographic apparatus. The planarizationlayer is desirably sufficiently thick to fill-in most or all of theroughnesses of the surface of the substrate holder. If the planarizationlayer is too thick, it is more likely to crack during curing. Applyingthe planarization layer in a plurality of separate coats, as describedbelow, can reduce the chance of such cracking and reduce the surfaceroughness of the final layer.

In an embodiment, the planarization layer is applied by coating thesubstrate holder 100 with a polysilazane solution which is then cured toform the silicon-based planarization layer. The reaction involved isshown in FIG. 16. In an embodiment, the polysilazane solution is appliedby a spray technique. Additionally or alternatively, other techniquessuch as spin coating can be used. FIGS. 17 to 19 depict other reactionsthat can be used to form planarization layers in embodiments of theinvention. FIG. 17 depicts a reaction that proceeds via an aqueousmedium alone. FIG. 18 depicts a reaction that proceeds in an aqueousmedium in the presence of heat. FIG. 19 depicts another reaction thatproceeds in an aqueous medium in the presence of heat. In each of FIGS.17 to 19, R depicts a functional group selected from the groupconsisting of hydrogen, methyl, fluoro. Note that in the chemicalreactions in FIGS. 16 to 19 the conversion of polysilazane with chainsof —Si—N— backbones to Si—O— backbones may not complete, i.e. reach100%. A resulting planarization layer after curing may have a lowconcentration of —Si—N— chains.

The planarization layer provides a surface that is sufficiently smoothfor reliable formation of one or more metal or other layers to form athin film component. In particular, glass bonding steps that may berequired with some materials used to form a substrate holder may beunnecessary.

FIGS. 9 and 10 illustrate steps in an embodiment of a method of applyingthe planarization layer 108. As shown in FIG. 9, the polysilazanesolution is sprayed across the upper surface 107 of the substrate holder100 and cured to form a continuous layer 108. This layer initiallycovers the burls 106 as well as the spaces between them. In a secondstep, the result of which is shown in FIG. 10, the planarization layer108 is removed from the top of the burls 106. This removal step can beperformed using a known technique, such as machining (lapping orpolishing), a chemical process (such as etching) with a laser and/orchemical mechanical polishing (CMP). This method has an advantage thatit is quick, involving only two steps.

FIGS. 11 to 14 illustrate steps in a further embodiment of a methodapplying the planarization layer 108. In this method, a photoresist 110is applied to the whole of the upper surface 107 of the substrate holder100. The photoresist is then selectively exposed and the exposed orunexposed photoresist, depending on whether the photoresist is positiveor negative, is removed, so that photoresist 110 remains only coveringthe burls 106 as shown in FIG. 12. In an embodiment the photoresistpossess an antiwetting function in order to guide the planarizationmaterial onto the surface between the burls 106. Planarization material108 is then applied, as shown in FIG. 13. Finally, the remainingphotoresist is removed to leave planarization material 108 only in thespaces between the burls 106.

In both of the above methods, the planarization layer 108 can be appliedin multiple coating steps in order to reduce the surface roughness. FIG.15 is a graph showing roughness values Ra in μm for planarization layersof four samples, numbered 1 to 4, of substrate holders according to anembodiment of the present invention. The substrate holder was of a SiSiCmaterial and as shown as A in FIG. 5 had a surface roughness Ra prior toany coating or other treatment of 2.45 μm. The samples were then spraycoated with a polysilazane solution (CAG 37 obtained from ClariantAdvanced Materials GmbH) and allowed to dry. In the case of samples 1and 3, the amount of solution applied was sufficient to achieve a layerthickness of 2.4 μm. In the case of samples 2 and 4 a greater amount wasapplied to achieve a layer thickness of 4 μm. After curing, the surfaceroughness Ra of samples 1 and 3 was measured at 1.04 μm and that ofsamples 2 and 4 as 1.05 μm, as shown at B in FIG. 15.

Before a second layer was applied, the first layers were hydrophillisedby exposing them to air plasma for approximately 1 minute. This step canbe omitted if only a single layer is to be applied or if the materialapplied is not hydrophobic. The amounts of material applied to form thesecond layer were varied. Samples 1 and 2 had an amount of solutionapplied to form a coating of 2.4 μm while samples 3 and 4 had an amountof solution applied to form a coating of thickness 4 μm. After curing ofthe second coating, the roughness Ra values of samples 1 to 4 weremeasured respectively at 0.37 μm, 0.46 μm, 0.63 μm and 0.44 μm, as shownat C in FIG. 15. From these results, an improved surface roughness maybe achieved by a two-step coating technique and it may be desirable thatthe thickness of a second coating layer is not greater than thethickness of a first applied coating layer.

Layer thicknesses and measured roughnesses are shown in the followingtable:

Sample: 1 2 3 4 1st Coating Thickness (μm) 2.4 4 2.4 4 2nd CoatingThickness (μm) 2.4 2.4 4 4 Uncoated Roughness Ra (μm) 2.45 2.45 2.452.45 Roughness Ra (μm) after one coat 1.04 1.05 1.04 1.05 Roughness Ra(μm) after two coats 0.37 0.46 0.63 0.44

Roughness values given above where obtained using a Taylor Hobson stylusprofiler having a diamond tip of radius 2 μm, which is scanned over thelayer to measure its profile and Ra is estimated from the contour map.Other equivalent instruments and methods can be used instead.

As will be appreciated, any of the above described features can be usedwith any other feature and it is not only those combinations explicitlydescribed which are covered in this application.

In an embodiment, there is provided a substrate holder for use in alithographic apparatus, the substrate holder comprising: a main bodyhaving a surface; a plurality of burls projecting from the surface andhaving end surfaces to support a substrate; and a planarization layerprovided on at least part of the main body surface.

In an embodiment, the planarization layer has a surface roughness Raless than about 1.5 μm, less than about 1.0 μm, or less than about 0.5μm. In an embodiment, the planarization layer is formed of asilicon-based material, for example formed from an organic precursor. Inan embodiment, the planarization layer is formed of a silicon oxide orsilicon nitride based material. In an embodiment, the planarizationlayer includes a functional group selected from the group consisting of:hydrogen, methyl, fluoro, vinyl and the like. In an embodiment, theplanarization layer is formed of an carbon-based material such asbenzocyclobutene. In an embodiment, the main body is formed of amaterial selected from the group consisting of: SiC (silicon carbide),SiSiC (siliconised silicon carbide), Si₃N₄ (silicon nitrite), quartz,and Zerodur™ glass ceramic. In an embodiment, the planarization layer isformed of a plurality of separately formed sub-layers. In an embodiment,the planarization layer has a thickness in the range of from about 0.2μm to about 200 μm. In an embodiment, the planarization layer does notcover at least the end surfaces of the burls. In an embodiment, theburls have side surfaces and the planarization layer does not cover atleast part of the side surfaces of the burls, desirably does not coverall of the side surfaces of the burls. In an embodiment, the substrateholder further comprises an electronic component provided on theplanarization layer. In an embodiment, the electronic component is athin-film component. In an embodiment, the electronic component is acomponent selected from the group consisting of: an electrode, a heater,and a sensor. In an embodiment, the electrode is, in use, an electrodeof an electrostatic clamp.

In an embodiment, there is provided a lithographic apparatus,comprising: a support structure configured to support a patterningdevice; a projection system arranged to project a beam patterned by thepatterning device onto a substrate; and a substrate holder arranged tohold the substrate, the substrate holder comprising: a main body havinga surface, a plurality of burls projecting from the surface and havingend surfaces to support a substrate, and a planarization layer providedon at least part of the main body surface.

In an embodiment, the planarization layer has a surface roughness Raless than about 1.5 μm, less than about 1.0 μm, or less than about 0.5μm. In an embodiment, the planarization layer is formed of asilicon-based material. In an embodiment, the planarization layer isformed of a silicon oxide or silicon nitride based material. In anembodiment, the planarization layer includes a functional group selectedfrom the group consisting of: hydrogen, methyl, fluoro, vinyl and thelike. In an embodiment, the planarization layer is formed ofbenzocyclobutene. In an embodiment, the main body is formed of amaterial selected from the group consisting of: SiC (silicon carbide),SiSiC (siliconised silicon carbide), Si₃N₄ (silicon nitrite), quartz,and Zerodur™ glass ceramic. In an embodiment, the planarization layer isformed of one or more of separately formed sub-layers. In an embodiment,the planarization layer has a thickness in the range of from about 0.2μm to about 200 μm. In an embodiment, the planarization layer does notcover at least the end surfaces of the burls. In an embodiment, theburls have side surfaces and the planarization layer does not cover atleast part of the side surfaces of the burls, desirably does not coverall of the side surfaces of the burls. In an embodiment, thelithographic apparatus further comprises an electronic componentprovided on the planarization layer. In an embodiment, the electroniccomponent is a thin-film component. In an embodiment, the electroniccomponent is a component selected from the group consisting of: anelectrode, a heater, and a sensor. In an embodiment, the electrode is,in use, an electrode of an electrostatic clamp. In an embodiment, thelithographic apparatus further comprises a substrate table and whereinthe substrate holder is integrated into the substrate table.

In an embodiment, there is provided a device manufacturing method usinga lithographic apparatus, method comprising: projecting a beam patternedby a patterning means onto a substrate; whilst holding a substrate in asubstrate holder; wherein the substrate holder comprising: a main bodyhaving a surface; a plurality of burls projecting from the surface andhaving end surfaces for supporting a substrate; and a planarizationlayer provided on at least part of the main body surface.

In an embodiment, there is provided a method of manufacturing asubstrate holder for use in a lithographic apparatus, the methodcomprising: providing a main body having a surface and a plurality ofburls projecting from the surface and having end surfaces to support asubstrate; and forming a planarization layer on at least part of themain body surface.

In an embodiment, the planarization layer is formed so as to have asurface roughness Ra less than about 1.5 μm, less than about 1.0 μm, orless than about 0.5 μm. In an embodiment, the planarization layer isformed of a silicon-based material. In an embodiment, the planarizationlayer is formed of a silicon oxide or silicon nitride based material. Inan embodiment, the planarization layer includes a functional groupselected from the group consisting of: hydrogen, methyl, fluoro, vinyland the like. In an embodiment, the planarization layer is formed ofbenzocyclobutene. In an embodiment, the main body is formed of amaterial selected from the group consisting of SiC (silicon carbide),SiSiC (siliconised silicon carbide), Si₃N₄ (silicon nitrite), quartz,and Zerodur™ glass ceramic. In an embodiment, the planarization layer isformed of one or more of separately formed sub-layers. In an embodiment,the planarization layer has a thickness in the range of from about 0.2μm to about 200 μm. In an embodiment, the planarization layer does notcover at least the end surfaces of the burls. In an embodiment, theburls have side surfaces and the planarization layer does not cover atleast part of the side surfaces of the burls, desirably does not coverall of the side surfaces of the burls. In an embodiment, the methodfurther comprises an electronic component provided on the planarizationlayer. In an embodiment, the electronic component is a thin-filmcomponent. In an embodiment, the electronic component is a componentselected from the group consisting of: an electrode, a heater, and asensor. In an embodiment, the electrode is, in use, an electrode of anelectrostatic clamp. In an embodiment, wherein the providing the mainbody having a plurality of burls comprises providing a blank andremoving material from the blank to leave the projecting burls. In anembodiment, the removing material is performed by a method selected fromthe group consisting of: electrical discharge machining, laser ablation,and etching. In an embodiment, the forming a planarization layercomprises applying a solution of polysilazane to the main body andcuring the solution to form the planarization layer.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications in manufacturing components with microscale, or evennanoscale features, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

The controllers described above may have any suitable configuration forreceiving, processing, and sending signals. For example, each controllermay include one or more processors for executing the computer programsthat include machine-readable instructions for the methods describedabove. The controllers may also include data storage medium for storingsuch computer programs, and/or hardware to receive such medium.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above, whether the immersion liquid is provided in the form ofa bath, only on a localized surface area of the substrate, or isunconfined on the substrate and/or substrate table. In an unconfinedarrangement, the immersion liquid may flow over the surface of thesubstrate and/or substrate table so that substantially the entireuncovered surface of the substrate table and/or substrate is wetted. Insuch an unconfined immersion system, the liquid supply system may notconfine the immersion liquid or it may provide a proportion of immersionliquid confinement, but not substantially complete confinement of theimmersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more liquid inlets, one ormore gas inlets, one or more gas outlets, and/or one or more liquidoutlets that provide liquid to the space. In an embodiment, a surface ofthe space may be a portion of the substrate and/or substrate table, or asurface of the space may completely cover a surface of the substrateand/or substrate table, or the space may envelop the substrate and/orsubstrate table. The liquid supply system may optionally further includeone or more elements to control the position, quantity, quality, shape,flow rate or any other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A substrate holder for use in a lithographic apparatus, the substrateholder comprising: a main body having a surface; a plurality of burlsprojecting from the surface and having end surfaces to support asubstrate; and a planarization layer provided on at least part of themain body surface.
 2. The substrate holder according to claim 1, whereinthe planarization layer has a surface roughness Ra less than about 1.5μm.
 3. The substrate holder according to claim 1, wherein theplanarization layer is formed of a silicon-based material.
 4. Thesubstrate holder according to claim 3, wherein the planarization layeris formed of a silicon oxide or silicon nitride based material.
 5. Thesubstrate holder according to claim 3, wherein the planarization layerincludes a functional group selected from the group consisting of:hydrogen, methyl, fluoro, vinyl and the like.
 6. The substrate holderaccording to claim 1, wherein the planarization layer is formed of acarbon-based material.
 7. The substrate holder according to claim 7,wherein the planarization layer is formed of benzocyclobutene.
 8. Thesubstrate holder according to claim 1, wherein the main body is formedof a material selected from the group consisting of: SiC (siliconcarbide), SiSiC (siliconised silicon carbide), Si₃N₄ (silicon nitrite),quartz, and Zerodur™ glass ceramic.
 9. The substrate holder according toclaim 1, wherein the planarization layer is formed of a plurality ofseparately formed sub-layers.
 10. The substrate holder according toclaim 1, wherein the planarization layer has a thickness in the range offrom about 0.2 μm to about 200 μm.
 11. The substrate holder according toclaim 1, wherein the planarization layer does not cover at least the endsurfaces of the burls.
 12. The substrate holder according to claim 11,wherein the burls have side surfaces and the planarization layer doesnot cover at least part of the side surfaces of the burls.
 13. Thesubstrate holder according to claim 1, further comprising an electroniccomponent provided on the planarization layer.
 14. The substrate holderaccording to claim 13, wherein the electronic component is a thin-filmcomponent.
 15. The substrate holder according to claim 13, wherein theelectronic component is a component selected from the group consistingof: an electrode, a heater, and a sensor.
 16. A lithographic apparatus,comprising: a support structure configured to support a patterningdevice; a projection system arranged to project a beam patterned by thepatterning device onto a substrate; and a substrate holder arranged tohold the substrate, the substrate holder comprising: a main body havinga surface, a plurality of burls projecting from the surface and havingend surfaces to support a substrate, and a planarization layer providedon at least part of the main body surface.
 17. The lithographicapparatus according to claim 16, wherein the planarization layer isformed of a silicon-based material.
 18. The lithographic apparatusaccording to claim 16, wherein the planarization layer is formed ofbenzocyclobutene.
 19. A method of manufacturing a substrate holder foruse in a lithographic apparatus, the method comprising: providing a mainbody having a surface and a plurality of burls projecting from thesurface and having end surfaces to support a substrate; and forming aplanarization layer on at least part of the main body surface.